The present invention relates to sprinklers and pertains more particularly to gear driven oscillating sprinklers.
In my prior U.S. Pat. No. 3,107,056 issued Oct. 15, 1963, entitled "SPRINKLER", I disclose a gear driven oscillating pop up type sprinkler. In that patent the drive train includes a shifting mechanism that alternately shifts a pair of terminal gears carried on a shifting plate into and out of engagement with an internal gear at the ends of the oscillating stroke. In adapting that drive system to more compact higher pop up stroke higher volume sprinklers, certain problems with the shifting mechanism were encountered.
The chief difficulty encountered was the different engaging and shifting forces present in the shifting mechanism. The shifting mechanism has a very strong self-engaging force when turning in the same direction as the input drive. A great deal of force is required to disengage the drive and shift to the opposite direction. The torque of the input gear to the shifting mechanism adds to the force that tends to hold the assembly into engagement and adds to the force required to disengage the gears at the end of the stroke. However, when rotating in the opposite direction, that is the ring gear is rotating in the direction opposite that of the input drive gear, the torque of the input gear tends to disengage the terminal gear driving it in that direction from the ring.
It has been found that these forces are affected by the pressure angle of the mating teeth between the driving pinions and the ring gear.
It is therefore desirable that an improved drive train be available which properly balances the engaging and disengaging forces of the shift and drive assembly.